Hello,
Just to say a customer of ours went across this issue, I found this topic with no solution, so I'm sharing what I foud:
It turned out they were logging in using a simple user rather than their main customer account, therefore they didn't have the permission to manage SSL certificates...
Hi,
Some paid themes and probably some plugins as well use their own repositories and are not available on WP repositories, like Hueman Pro which I use.
Therefore, Plesk's WP toolkit is unable to update these, you can only update them by logging into the website and updating them the basic...